Browsing by Author "Sophia Kathariou, Committee Chair"

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Antimicrobial Susceptibility Profiles and Clonal Population of Multidrug Resistant Campylobacter coli Isolates from Commercially Grown Turkeys.
(2011-02-04) Ahmad, Harun; Sophia Kathariou, Committee Chair; Jonathan Allen, Committee Member; Donna Carver, Committee Member; Deborah Threadgill, Committee Member; Sophia Kathariou, Committee Member
Campylobacter Colonization in Turkey Flocks Reared in North Carolina
(2003-07-11) Smith, Katie Sullivan; Sophia Kathariou, Committee Chair
Campylobacter spp are currently the leading cause of foodborne acute bacterial gastroenteritis in people in industrialized countries. It is estimated by the Centers for Disease Control and Prevention that Campylobacter accounts for 2.4 million human cases of gastroenteritis annually in the United States. The main risk for acquiring Campylobacter infection is handling raw poultry and/or consumption of undercooked meat of animal origin, particularly poultry. Research concerning Campylobacter in poultry has been focused on broilers; little information is available on the colonization of turkeys. Consumption of turkey products has increased considerably in recent years; therefore, there is a need to focus attention on this potential vehicle of campylobacteriosis. First, a longitudinal study was conducted on two pairs of sibling turkey flocks obtained from the same hatch that shared a common breeder source. One flock from each pair was raised commercially whereas the other was raised under contract at the Teaching Animal Unit (TAU) at the North Carolina State University Veterinary School. Time of placement, feed formulations, and bird density were the same among the members of each pair. At the completion of the production cycle, birds of each flock were processed in commercial processing plants, following standard feed withdrawal and transport protocols. Both commercial flocks became colonized at 2 to 3 weeks of age and remained colonized through processing while the flocks raised at the TAU remained free of Campylobacter until processing. In addition to prevalence of Campylobacter spp. other epidemiological factors of interest in this study were antibiotic resistance profiles, species colonizing the birds, and strain types present throughout the life of the birds. The turkeys were predominantly colonized by C. coli (84-88%) with C. jejuni accounting for the remainder of the isolates. Both commercial flocks were colonized by a limited number of strains with one dominant strain being isolated throughout the life of the bird. C. coli isolates were resistant to a variety of antibiotics including erythromycin and fluoroquinolones. C. jejuni isolates were also resistant, but were more likely to be sensitive to erythromycin and fluoroquinolones. These results indicate that vertical transmission, if occurring, was not sufficient for colonization of these turkey flocks by Campylobacter and points towards the important role of flock management in preventing colonization. In addition, the turkeys were colonized by one main strain type which could be due to selective pressures related to antibiotic treatments. The level of antibiotic resistance in both the C. coli and C. jejuni isolates is of definite food safety concern. The high prevalence of C. coli in the turkeys was unexpected and developed an interest in evaluating broilers raised in the same geographical region to determine if they also were predominantly colonized by C. coli. A cross-sectional survey was conducted on 32 farms from 2 broiler integrators in the same region. Sixteen of 32 farms had flocks that were colonized with Campylobacter at 4 weeks of age. Of these 16 flocks, 10 were primarily colonized by C. jejuni whereas 5 flocks were predominantly colonized by C. coli. No samples could be purified from one of the Campylobacter-positive flocks. There was a high level of resistance in both the C. jejuni and C. coli isolates to several antibiotics including those that are used to treat human illnesses. Resistance to multiple antibiotics was more common in the turkey isolates. However, fluoroquinolone resistance was more prevalent in the broiler isolates. These findings indicate that broilers in eastern North Carolina were primarily colonized by C. jejuni and that the high prevalence of C. coli colonization that we observed in the commercial turkey flocks that we studied was likely not related to the specific geographic region. A possible explanation for the prevalence of C. coli in the turkeys is that integrators in North Carolina often raise turkeys as well as hogs, which are typically colonized by C. coli. This is not a common practice for broiler integrators. Thus, the prevalence of C. coli in turkeys is more likely to be dependent upon practices within the turkey industry in N. Carolina rather than geographic region.
Efficacy of Naturally Occurring Antimicrobials to Reduce Salmonella spp. Associated with Poultry at Various Stages of Processing.
(2010-12-09) Sybirtseva, Iryna; Sophia Kathariou, Committee Chair; Fletcher Arritt, Committee Chair; John Luchansky, Committee Member; Karina G. Martino, Committee Member; Dana Hanson, Committee Member; Douglas Smith, Committee Member
Erythromycin Susceptibility and Genomic Regions Characterization of Campylobacter coli
(2007-11-01) Chan, Kamfai; Todd Klaenhammer, Committee Member; Fred Breidt, Committee Member; Sophia Kathariou, Committee Chair; Craig Altier, Committee Member
Campylobacter jejuni and Campylobacter coli are major bacterial food-borne pathogens that cause enteric diseases worldwide, resulting in significant public health and economic burden. These two closely related species colonize a wide range of farm animals including turkeys, pigs, chickens, and cattle. Consumption of meat (especially poultry) contaminated with C. jejuni or C. coli has been implicated as the major route of infection. When needed, antibiotics used for treatment are fluoroquinolones or macrolides such as erythromycin. Recent studies have shown that the percentage of C. coli that have resistance to antimicrobials, including those typically used for treatment of human campylobacteriosis, has increased, making it a top priority to investigate the mechanisms for acquisition and dissemination of antimicrobial resistance in these pathogens. Certain Campylobacter strains harbor a transcribed intervening sequence (IVS) in their 23S rRNA genes. Following transcription, the IVS is excised, leading to fragmentation of the 23S rRNA. The origin and possible functions of the IVS are unknown. Furthermore, the distribution of IVS-harboring strains within Campylobacter populations is poorly understood. In this study, strains of Campylobacter coli from turkeys, representing numerous different multilocus sequence typing (MLST)-based sequence types (STs), were characterized in terms of IVS content and erythromycin susceptibility. We identified strains that harbored IVSs in all three 23S rRNA genes, as well as strains lacked IVSs from at least one of the genes. The STs of the latter strains belonged to an unusual cluster of C. coli STs ('cluster II'), earlier found primarily in turkey strains, and characterized by presence of the C. jejuni aspA103 allele. The majority of strains harboring IVSs in all three 23S rRNA genes were resistant to erythromycin. In contrast, cluster II strains, which harbored at least one IVS-free 23rRNA gene, were susceptible to the antibiotic. Cluster II strains could be transformed to erythromycin resistance with genomic DNA from C. coli that harbored IVS and the A2075G transition in the 23S rRNA gene, associated with resistance to erythromycin in Campylobacter. Erythromycin-resistant transformants harbored both the A2075 transition and IVS. The findings suggest that absence of IVS in C. coli from turkeys is characteristic of a unique clonal group of erythromycin-susceptible strains, and that IVS can be acquired by these strains via natural transformation to erythromycin resistance. Analysis of C. coli and C. jejuni strains isolated from broilers, turkeys and swine has shown the association of the lack of IVS and erythromycin susceptibility is unique to C. coli from turkeys. The presence of the C. jejuni aspA103 allele in the chromosome of cluster II C. coli strains is a unique characteristic of this clonal group. To further characterize the genome composition in the aspA region in cluster II strains, we determined the corresponding DNA sequences from two turkey-derived cluster II C. coli strains (6979 and 7474, of ST-1150 and ST-1161, respectively). Genomic organization upstream of the aspA gene was divergent between these two cluster II strains and the reference strain C. coli RM2228, the genome sequence of which has been completed. Genes encoding a putative Crp-family transcriptional regulator (CCO0137) and a conserved hypothetical protein (CCO0138) that were present in C. coli RM2228 and C. coli 6818 were not found in the same genomic region in C. coli 6979 or C. coli 7474. Moreover, single nucleotide polymorphism (SNP) analysis revealed that genes encoding subunit II of cytochrome d ubiquinol oxidase (cydB) and a putative aspartate racemase (CJ0085c) harbored numerous C. jejuni-specific SNPs. Interestingly, genes encoding subunit I of cytochrome d ubiquinol oxidase (cydA) and uracil-DNA glycosylase (ung) harbored C. coli-specific SNPs in their 5' portions but C. jejuni-specific SNPs in their 3' portions, suggesting that these may be hybrid genes that were originated from C. jejuni and C. coli. Our data suggest the presence of recombination events in the genomic region between cydA and ung in cluster II strains of C. coli. Such genomic features may contribute to the observed prevalence of cluster II strains among C. coli from turkeys, and to the characteristic susceptibility to erythromycin exhibited by these strains.
Gene Cassettes Unique to Epidemic-associated Lineages of Listeria monocytogenes serotype 4b
(2006-03-02) Yue, Lili; Eric Miller, Committee Member; Jenny Xiang, Committee Member; Sophia Kathariou, Committee Chair
Listeria monocytogenes is responsible for severe foodborne infections, with high mortality and morbidity. A clonal group of L. monocytogenes strains of serotype 4b designated Epidemic Clone I (ECI) has been responsible for numerous outbreaks of foodborne illness in the United States and elsewhere. A number of genes and gene cassettes unique to ECI strains have been identified through molecular approaches, and through the recently completed genome sequencing on ECI strain. However, the functions of most of these ECI specific sequences remain unclear. The purpose of this research has been to perform a comparative genomic analysis of the regions harboring four ECI specific gene cassettes, designated region 144, 133, 17B and 85, among five different Listeria strains for which genome sequencing projects have been undertaken. The strains included ECI strain F2365 (serotype 4b), ECII strain H7858 (serotype 4b), serotype 1/2a strains EGD-e and F6854, and Listeria innocua CLIP 11262. The genomic organization of the region harboring these cassettes in ECI was investigated in the different genomes, and transcriptional analysis by reverse-transcriptase polymerase chain reaction was pursued with three regions, 144, 133 and 17B. The comparative genomic organization data revealed that all four ECI specific regions have features typical of genomic islands (GEIs), being present in the genome of ECI strains but absent from the genome of other serotype 4b strains, suggesting horizontal insertion / deletion events and possible roles in pathogenicity and metabolism of the organism. Transcriptional data suggested that the six ECI specific open reading frames in region 133 were co-transcribed as a unit separate from adjacent genes which were highly conserved among different strains. To obtain information on the possible functions of the ECI specific genes and gene cassettes, a mutational approach was pursued. A deletion mutant of the ECI specific sequence in region 133 was constructed in two different ECI strains, and the mutants were characterized bacteriologically and in terms of phenotypic microarrays. The deletion mutant F2365 ∆133 was characterized in terms of basic bacteriological features including hemolytic activity, phage susceptibility, motility, cell morphology, growth at 37°C, 25°C and 4°C, bacitracin resistance, surface antigen detection, and with a panel of phenotypic microarrays. The parental strain F2365 was observed to grow better than the deletion mutant F2365 ∆133 at 4°C, and the Phenotypic Microarrays identified certain differences in substrate utilization between the mutant and the wild type parental strain. The findings suggest that the ECI specific cassette in region 133 may contribute to bacterial growth at cold temperature and to the metabolism of certain carbon and nitrogen sources. Future studies employing animal and cell culture models will be needed to evaluate the possible impact of the ECI specific cassette in region 133 in virulence and pathogenesis of the bacteria.
Genetic characterization of Multidrug resistant strains of Campylobacter coli from turkeys in North Carolina
(2007-08-06) D'lima, Carol Bonnie; Dahlia Nielsen, Committee Member; Fred Breidt, Committee Member; James Brown, Committee Member; Donna Carver, Committee Member; Sophia Kathariou, Committee Chair
Commercial turkey flocks in North Carolina are frequently colonized with Campylobacter coli strains that are resistant to several antimicrobials and have been designated multidrug resistant (MDR). Multiple locus sequence typing (MLST) showed that the major sequence types (STs) were turkey-specific. Further subtyping using fla typing, pulsed field gel electrophoresis (PFGE) with SmaI and KpnI as well as plasmid profiles revealed that each of the major MDR STs contained strains of related, but distinct subtypes, providing evidence for genomic diversification within these STs. Numerous strains, with indistinguishable PFGE profiles, but different fla types suggested selection for specific flagellin sequences. The observed correlation between STs and the MDR profiles of the microbes indicates that MLST-based typing holds potential for source-tracking applications specific to the animal source (turkeys) and the antimicrobial resistance profile (MDR) of C. coli. The molecular basis for resistance of MDR strains to selected antimicrobials was investigated, and tetracycline resistant isolates were shown to harbor tet(O). Natural transformation studies were used to study the mechanism of transfer of antibiotic resistance genes in C. coli. Resistance to erythromycin and nalidixic acid/ciprofloxacin mediated by chromosomal sequences, were easily transferred from MDR strains to other C. coli, whereas resistance to tetracycline and kanamycin was not possible by transformation, suggesting that genes mediating these resistance attributes were plasmid-borne in MDR strains. Interestingly, tetracycline resistance could be readily transferred by transformation using DNA from another clonal group of C. coli strains prevalent in turkeys, suggesting chromosomal presence of the tetracycline resistance gene. MDR strains were found to be stable and maintained their MDR phenotype over 60 serial passages in vitro. The strains maintained their PFGE and plasmid profiles; and only minor differences in MICs before and after the 60 passages were observed. The findings from this study suggest that the certain strain types and clonal groups are prevalent among MDR C. coli from turkeys, and that resistance determinants to certain antibiotics can be transferred from these MDR strains to other C. coli strains.
Molecular Characterization of Listeria monocytogenes Epidemic Clone I (ECI) like isolates from Food and Food Environments
(2007-08-08) Yildirim, Suleyman; Jeffrey Thorne, Committee Member; Craig Altier, Committee Member; Sophia Kathariou, Committee Chair; Lee-Ann Jaykus, Committee Co-Chair; Todd R Klaenhammer, Committee Member
Natural Transformation-mediated Transfer of Erythromycin Resistance in Campylobacter coli and Campylobacter jejuni
(2005-11-09) Kim, Joo-Sung; Sophia Kathariou, Committee Chair; Fred Breidt, Committee Member; Donna K. Carver, Committee Member; Paul Orndorff, Committee Member
Campylobacter is the most common bacterial agent causing human gastroenteritis and is mainly transmitted through foods. Campylobacter is a zoonotic agent, and commonly colonizes poultry and other meat animals. Whereas erythromycin resistance in Campylobacter jejuni rarely occurs, erythromycin resistance in Campylobacter coli from meat animals is frequently encountered, and could represent a substantial barrier to antibiotic treatment of human infections. Erythromycin resistance in C. coli has been associated with a point mutation (A2075G) in the 23S rRNA gene, acting synergistically with the CmeABC efflux pump. However, the mechanisms responsible for possible dissemination of erythromycin resistance in C. coli remain poorly understood. In this study we investigated transformation-mediated acquisition of erythromycin resistance by genotypically diverse C. coli strains from turkeys and swine, with total genomic DNA from erythromycin-resistant C. coli used as donor. In addition, we studied the effects of environmental factors and species (C. coli vs. C. jejuni), and fitness costs of erythromycin resistance in transformants. Overall, transformation to erythromycin resistance was significantly more frequent in C. coli from turkeys than in swine-derived strains (P<0.01) with frequency of transformation 10⁻⁻⁴ to 10⁻⁶ in turkey-derived strains, but 10⁻⁷ or less in C. coli from swine. Transformants harbored the point mutation, A2075G in the 23S rRNA gene. Erythromycin resistance was stable in transformants following serial transfers, and most transformants had high MIC values (>256μg/ml), as did the C. coli donor strains. In contrast to results obtained with transformation, spontaneous mutants had relatively low erythromycin MIC (32-64μg/ml) and lacked the A2075G mutation. Temperature profoundly affected frequency of transformation to erythromycin resistance in C. coli and transformation frequency at 42°C was significantly higher than at 25°C, 32°C and even 37°C. However, transformation to nalidixic acid resistance was not significantly affected by temperature. No significant difference in transformation frequency was detected between microaerobic (5-10% CO₂) and aerobic conditions. Starvation conditions did not affect transformation frequency to nalidixic acid resistance. Increasing incubation time from 3-4h to 15-17h significantly increased transformation frequency to erythromycin resistance (P<0.05). Transformation of C. jejuni using genomic DNA from erythromycin resistant C. coli revealed that transformation frequency of C. jejuni to erythromycin resistance was lower than C. coli, suggesting that erythromycin resistance in C. coli may not be disseminated via transformation in C. jejuni as frequently as in C. coli. Transformants derived from C. jejuni, however, had high erythromycin MIC values (>256μg/ml) and harbored the A2075G transition, similarly to C. coli transformants. When grown separately at 42°C, an erythromycin-resistant transformant derived from C. coli strain 961 had a similar growth rate as its erythromycin-sensitive parental strain, whereas an erythromycin-resistant transformant derived from C. jejuni strain SC49 had a significantly longer generation time compared to its parental strain. In competitive growth studies, however, the C. coli transformant was at competitive disadvantage in relation to its parental strain in stationary phase, whereas the C. jejuni transformant was at a slight fitness advantage after 14days. Furthermore, in the mixed culture the generation time of the C. jejuni transformant was not significantly different from that of the parental strain. In conclusion, natural transformation has the potential to contribute to dissemination of high-level resistance to erythromycin among C. coli strains colonizing meat animals and temperature can greatly affect transformation to erythromycin resistance, but not to nalidixic acid resistance. These findings suggest that ecological attributes may play an important role and exert differential impact on the potential of the organism to acquire antimicrobial resistance determinants via natural transformation. However, further study is necessary to characterize the fitness of erythromycin resistant transformants in Campylobacter and identify possible mechanisms underlying the relatively low frequency of erythromycin resistance in C. jejuni.
Phenotypic and genetic characterization of Listeria monocytogenes from the environment of turkey processing plants
(2009-01-11) Mullapudi, Savitri; Jonathan C. Allen, Committee Member; Lee-Ann Jaykus, Committee Member; Sophia Kathariou, Committee Chair
Resistance of clinical strains of Listeria monocytogenes to heavy metals, especially cadmium and arsenic has been used extensively for subtyping. Furthermore, the three most recent multistate outbreaks of listeriosis in the United States (1998-99 hot dog outbreak, and outbreaks in 2001 and 2002) have involved cadmium resistant strains two of which (1998-99 and 2001) were resistant to the quaternary ammonium disinfectant benzalkonium chloride (BC) as well. In these outbreak strains, genes mediating cadmium and BC resistance were found to be localized in two different gene cassettes on large plasmids (ca. 80 kb). However, limited information has been available on resistance to cadmium, arsenic and BC among L. monocytogenes isolates from the food processing plant environment. It is not known whether resistance to heavy metals (cadmium and arsenic) and BC is plasmid-borne in such strains and whether resistance to cadmium and arsenic may be correlated to resistance to disinfectants commonly used in the processing plant environment. Furthermore, information regarding contamination patterns of turkey processing plants in the United States with regards to different serotypes and strain types of L. monocytogenes is currently inadequate. In this study, we characterized 123 L. monocytogenes isolates (53 of serotype 1/2a or 3a, 39 of serotype 1/2b or 3b, and 27 of the serotype 4b complex, consisting of serotype 4b and the closely related serotypes 4d and 4e, and 4 strains of serotype 1/2c or 3c) from the environment of six turkey processing plants in the United States for cadmium, arsenic and BC resistance. In addition, these isolates were subtyped using pulsed field gel electrophoresis (PFGE). Moreover we investigated the prevalence among these isolates of three different cadmium resistance cadA determinants identified to date in L. monocytogenes: cadA1 (associated with Tn5422), cadA2 (associated with plasmid pLM80, identified in the 1998-99 outbreak strain), and cadA3, associated with the integrated conjugative element (ICE) of L. monocytogenes EGD-e, respectively). We employed plasmid curing protocols to examine if the resistance to heavy metals (cadmium and arsenic) and to BC was plasmid-borne and to assess the stability of cadmium and BC resistance among isolates of L. monocytogenes from the processing plant environment. Resistance to cadmium and BC was more common in serogroup 1/2 strains than 4b, whereas arsenic resistance was more commonly encountered in strains from the serotype 4b complex. We found substantial strain diversity in the turkey processing plants with 104 distinct PFGE types from 123 isolates using both enzymes (AscI and ApaI), resulting in Simpsonâ€™s index of diversity (D) of 0.995. Plant-specific strains were commonly found within each serotype. Heavy metal (cadmium and arsenic) and BC resistance were detected frequently among the serogroup 1 /2 strains. Our investigation has shown that 28% of the L. monocytogenes strains harbored both cadA1 and cadA2 and that the type of determinant (cadA1 vs. cadA2) may vary based on serotype as well as based on BC resistance (cadA2 being found more frequently among BC resistant than BC susceptible strains of the same serotype). The results also showed that the curing of plasmid borne cadmium and BC resistance was possible in certain strains isolated from the environment of turkey processing plants although the rate of plasmid loss was low. These results suggest that the processing plant environment may represent a reservoir for L. monocytogenes having resistance to cadmium and BC. Further studies are needed to elucidate the mechanisms underlying the prevalence of the different determinants, and their possible role in the ecology and evolution of L. monocytogenes in the processing plant environment. In addition, further studies need to be undertaken to confirm the location of the resistance determinants on plasmids, or possibly on the chromosome, especially in strains that failed to lose resistance following exposure to plasmid curing protocols.
Potential transfer of Campylobacter between turkeys and swine produced in close proximity, in eastern North Carolina
(2007-07-10) Wright, Sandra Lashawn; Morgan Morrow, Committee Member; William Flowers, Committee Member; Donna Carver, Committee Member; Sophia Kathariou, Committee Chair
Prevalence and Dissemination of Antimicrobial Resistance among Campylobacter jejuni and Campylobacter coli from Meat-Animals
(2009-12-02) Islam, Mohammed Shahidul; Jonathan Olson, Committee Member; Jonathan C. Allen, Committee Member; Sophia Kathariou, Committee Chair
Campylobacter jejuni and C. coli from conventionally grown turkeys have been frequently reported to be resistant to nalidixic acid and ciprofloxacin. To reduce possible contributions of fluoroquinolone use in poultry production to fluoroquinolone resistance in poultry-derived Campylobacter, use of the fluoroquinolone enrofloxacin (trade name, Baytril) was banned in July 2005. However, the impact of this ban on fluoroquinolone resistance in thermophilic campylobacters from turkeys has not been rigorously evaluated yet. In this study, we investigated prevalence of quinolone/fluoroquinolone resistance and multidrug resistance among 1552 Campylobacter isolates (81% C. coli and 19% C. jejuni) derived from 2371 cecal samples of young turkeys (10 days to six weeks of age). The isolates were derived from different flocks and farms, representing three different integrators, from 2002 to 2008. Resistance to ciprofloxacin and nalidixic acid was highly prevalent (585/722, 81%) among isolates from 2002 to August 2005, and prevalence was even higher (779/830, 94%) among isolates from 2006 to 2008, the three surveyed years subsequent to the ban (p<0.0001). Multidrug resistant C. coli (resistant to tetracycline, streptomycin, kanamycin, erythromycin, nalidixic acid and ciprofloxacin) and C. jejuni (resistant to all of the above except erythromycin) represented 46% and 66% of the campylobacters isolated in the periods prior to and subsequent to the enrofloxacin ban, respectively. Multidrug resistance prevalence increased significantly post-ban (p<0.0001) for both C. coli and C. jejuni. Ciprofloxacin MIC determinations suggested that there was no obvious difference in MIC distribution before and after the enrofloxacin ban. Our results suggest that there was no detectable decrease in prevalence of fluoroquinolone resistance among turkey-derived campylobacters within the surveyed three-year period following the enrofloxacin ban. Instead, and for reasons that remain unknown, prevalence values for fluoroquinolone resistance and for multidrug resistance were higher post-ban than pre-ban (p<0.0001). Continued surveys are needed to further evaluate the potential impact of the ban on resistance of campylobacters from turkeys to fluoroquinolones and other antibiotics. Even though fluorioquinolones are no longer permitted for use in poultry, several antimicrobials, for instance tetracycline, continue to be used extensively in conventional production. Naturally competent C. coli C. jejuni are able to acquire foreign DNA from different sources through transformation but the role of transformation in the dissemination of tetracycline resistance in Campylobacter has not been investigated. We therefore investigated transfer of tetracycline resistance from tetracycline resistant C. coli and C. jejuni to tetracycline-susceptible (TS) C. coli and C. jejuni derived from meat animals. Tetracycline-resistant (TR) but kanamycin susceptible (KS) C. coli both from turkey and swine could serve as donors in transformation-mediated transfer of tetracycline resistance to TS C. coli from turkeys. TR and kanamycin-resistant (KR) C. coli from turkeys were unable to serve as donors of tetracycline resistance whereas certain TR KR swine-derived strains successfully transformed tetracycline resistance. None of the TR KR C. jejuni strains could serve as donors and overall C. coli proved to be better donors in transforming tetracycline resistance than C. jejuni. However, a bovine TR KS C. jejuni donors strain was successful in transforming turkey-derived as well as bovine C. jejuni to tetracycline resistance. Further studies are needed to evaluate the impact of transformation in dissemination of tetracycline resistance among C. jejuni and C. coli from animal production systems.
Virulence Attenuation and Relative Fitness of Listeria monocytogenes from the Processing Plant Environment.
(2010-10-22) White, Sheea; Jonathan Allen, Committee Chair; Sophia Kathariou, Committee Chair; Charles Williams, Committee Member; Susan Carson, Committee Member; Larry Stikeleather, Committee Member